1. Field of the Invention
This invention is directed to a method and apparatus for reading and writing on magnetic recording media with a magneto-resistive head. More particularly, this invention relates to linearizing the transfer characteristic of the magneto-resistive head.
2. Description of Prior Art
The transfer characteristic of Magneto-Resistive (MR) recording heads in reading or writing signals on magnetic media is very dependent on the bias current applied to the recording head. The bias current sets the operating point of the head. If the operating point is in the most linear portion of the resistance variation with magnetic field, then the transfer characteristic from sensed magnetic field to output signal from the head will be substantially linear and free of distortion.
The prior art teaches various bias circuits for MR heads that are designed to set the optimum bias current for an MR head. U.S. Pat. No. 4,050,086 by J. D. Harr, and U.S. Pat. No. 4,712,144 by K. B. Klassen are each directed to a bias circuits for MR heads. The circuits are designed to set the bias current to compensate for manufacturing variations in the resistance of the heads. U.S. Pat. No. 3,979,775 issued to T. A. Schwarz uses an additional MR element and a bias circuit to compensate the MR head and its bias current for thermal drift.
The prior art compensates for manufacturing tolerances in the heads, it compensates for slow variations in the heads such as thermal drift, but the prior art does not teach a solution to the problem of controlling the MR heads dynamically in real time to keep them operating at the correct bias current for optimum performance.